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This invention relates to producing petroleum wells and more particularly to a system using the difference in fluid pressure across a packer in a producing well to provide power to downhole instruments or actuators.
The logging of oil and gas wells has been a standard practice for many years. Logging generally means placing an instrument in a borehole to measure various parameters to determine characteristics of the earth formations which have been drilled through. For instance, electrical resistivity of the earth formations may be measured as an indicator of whether the formations contain water or oil. Originally, logging could only be performed after the drill string, i.e. drill pipe and bit, was removed from the borehole. The logging instruments were normally supported by a wireline which provided mechanical support for the logging device in the borehole and provided electrical conductors to supply power to the device and to send signals between the device and equipment at the surface location of the well.
More recently, logging while drilling and measurement while drilling devices have been installed in the drill string to make measurements during the drilling process. While some of these devices require that drilling be stopped while measurements are taken, they avoid the expense of pulling the drill string out of the borehole. These devices provide information in real time, or near real time, and have proven beneficial during the drilling process. Since these devices must operate as part of an operating drill string, it has proven difficult or impractical to provide electrical conductors to supply power to the devices and communicate signals between the devices and equipment at the surface location of the well. Power is usually provided by batteries or mud driven downhole generators. Signals may be transmitted up and down hole by acoustic waves or pulses in the mud column or the drill pipe, all referred to herein as acoustic telemetry. Some systems use electromagnetic waves or pulses to transmit signals up and down hole, all referred to herein as electromagnetic or EM telemetry.
After drilling and logging a well, equipment may be installed for testing producing zones. For example a drill string or coiled tubing with an inflatable packer may be run down an uncased borehole to a location just above the producing zone. The packer may then be inflated to form a fluid seal between the tubing and the wall of the borehole. The well may then be produced for testing purposes through the drill string or coiled tubing. The drill string or coiled tubing acts as production tubing for the duration of the test.
After drilling, logging and testing of a successful well, equipment may be installed for permanent production of fluids, which process is referred to as completion of the well. In a simple completion, casing is cemented into a well down to and usually through the producing zone. In open hole completions, casing may be installed only in an upper portion of the borehole. If casing extends through the producing zone, it is normally perforated in the producing zone to allow fluids to flow into the well. Production tubing is placed inside the well down to the producing zone. The tubing normally has a packer at or near its lower end. After being properly positioned, the packer is actuated to form a fluid tight seal between the production tubing and the borehole which forces produced fluids to flow through the tubing. If casing extends to the producing zone, the packer will seal to the casing. For open hole completions the packer will seal to the inner wall of the borehole. The space or annulus between the production tubing and the borehole or casing is usually filled with a completion fluid usually comprising salt water.
It is often desirable to install instrumentation packages as part of a well test or a well completion. For example, pressure and temperature measurement devices may be installed in the well at the producing zone. These devices need electrical power to operate and to transmit signals up to the surface location of the well. While it is possible to install electrical conductors down the well to provide power and signal paths, it has proven to be difficult and expensive, especially in deep wells. Typically, batteries do not survive long in the high temperature conditions usually found in deep wells and it could be very expensive to replace depleted batteries.
In wells with multiple producing zones, a completion often includes multiple production tubing strings. It also may include control valves for each string so that flow from each zone may be controlled for various reasons. These control valves generally need a power source to operate. If control valves are controlled by acoustic or electromagnetic signals sent from the surface location to a receiver near the control valves, the receiver needs electrical power to operate. As with downhole instruments, it is often difficult or impractical to provide the power and signals to such valves over electrical conductors, especially in deep wells.
It would be desirable to provide a source of power to downhole instruments, signaling systems, actuators and other devices in producing wells without installing electrical cables in the well.
In accordance with the present invention, a downhole power system includes a conduit bypassing a packer sealing element and means for using pressure differential in the fluids above and below the packer to provide power to instruments and actuators installed in the well.
In one embodiment, the system includes a fluid driven motor driving an electrical generator and an electrical storage device. A controller monitors the status of the storage device and allows fluid from the conduit to flow to the motor when the storage device needs to be recharged.
In another embodiment, a controller switches fluid flow from the conduit to hydraulically driven actuators which mechanically drive mechanical devices such as flow control valves.